Copy the wasm exports object if we intend to modify it

.circleci/config.yml

@@ -167,7 +167,7 @@ test-chrome: &test-chrome
           # --no-sandbox becasue we are running as root and chrome requires
           # this flag for now: https://crbug.com/638180
           CHROME_FLAGS_BASE="--no-first-run -start-maximized --no-sandbox --use-gl=swiftshader"
-          CHROME_FLAGS_WASM="--enable-features=WebAssembly --enable-features=SharedArrayBuffer --disable-features=WebAssemblyTrapHandler --js-flags=\"--experimental-wasm-threads --harmony-sharedarraybuffer --no-wasm-disable-structured-cloning\""
+          CHROME_FLAGS_WASM="--enable-features=WebAssembly --enable-features=SharedArrayBuffer --disable-features=WebAssemblyTrapHandler --enable-experimental-web-platform-features --js-flags=\"--experimental-wasm-threads --harmony-sharedarraybuffer --no-wasm-disable-structured-cloning\""
           export EMTEST_BROWSER="xvfb-run -a -e /dev/stdout /usr/bin/google-chrome-stable $CHROME_FLAGS_BASE $CHROME_FLAGS_WASM"
           export EMTEST_LACKS_GRAPHICS_HARDWARE=1
           export EMCC_CORES=4

emscripten.py

@@ -1707,11 +1707,6 @@ def create_receiving(function_table_data, function_tables_defs, exported_impleme
 
   shared.Settings.MODULE_EXPORTS = module_exports = exported_implemented_functions + function_tables(function_table_data)
 
-  # Currently USE PTHREADS + EXPORT ES6 doesn't work with the previously generated assertions.
-  # ES6 modules disallow re-assigning read-only properties.
-  if shared.Settings.USE_PTHREADS and shared.Settings.EXPORT_ES6 and shared.Settings.ASSERTIONS and receiving:
-    receiving = "assert(!ENVIRONMENT_IS_PTHREAD, 'Error: USE_PTHREADS and EXPORT_ES6 requires ASSERTIONS=0');\n" + receiving
-
   if not shared.Settings.SWAPPABLE_ASM_MODULE:
     if shared.Settings.DECLARE_ASM_MODULE_EXPORTS:
       imported_exports = [s for s in module_exports if s not in initializers]

src/preamble.js

@@ -973,6 +973,14 @@ function createWasm(env) {
   // performing other necessary setup
   function receiveInstance(instance, module) {
     var exports = instance.exports;
+    // We want to modify the exports in some cases, however, in ES6 environments that
+    // may be illegal as the wasm exports are an ES6 export object, which is read-only.
+    // To work around that, we simply make a copy of them.
+#if EXPORT_ES6 && (ASSERTIONS || BYSYNCIFY)
+    var originalExports = exports;
+    exports = {};
+    for (var x in originalExports) exports[x] = originalExports[x];
+#endif
 #if BYSYNCIFY
     exports = Bysyncify.instrumentWasmExports(exports);
 #endif

tests/test_browser.py

@@ -4715,3 +4715,29 @@ def test_minimal_runtime_loader_shell(self):
       for modularize in [[], ['-s', 'MODULARIZE=1']]:
         print(str(args + wasm + modularize))
         self.btest('minimal_hello.c', '0', args=args + wasm + modularize)
+
+  @no_firefox('need to enable es6 modules there somehow')
+  def _test_es6(self, args):
+    args = args + ['-s', 'EXPORT_ES6', '-s', 'MODULARIZE', '-s', 'MODULARIZE_INSTANCE', '-s', 'ASSERTIONS', '-o', 'test.mjs']
+    print(args)
+    create_test_file('src.c', self.with_report_result(open(path_from_root('tests', 'browser_test_hello_world.c')).read()))
+    self.compile_btest(['src.c'] + args)
+    create_test_file('test.html', '''
+      <script type="module" src="test.mjs"></script>
+    ''')
+    self.run_browser('test.html', None, '/report_result?0')
+
+  def test_es6_O0(self):
+    self._test_es6([])
+
+  def test_es6_O3(self):
+    self._test_es6(['-O3'])
+
+  def test_es6_async(self):
+    self._test_es6(self.get_async_args())
+
+  @requires_threads
+  def test_es6_threads(self):
+    # TODO: use PROXY_TO_PTHREAD and/or '-s', 'PTHREAD_POOL_SIZE=1' once https://bugs.chromium.org/p/chromium/issues/detail?id=680046 is fixed
+    #       firefox also errors, "SyntaxError: dynamic module import is not implemented"
+    self._test_es6(['-s', 'USE_PTHREADS', '-s', 'PROXY_TO_PTHREAD'])